In the nonvolatile memory express (NVMe) system, a host device writes data storage device commands, such as read commands, write commands, and administrative commands, in submission queues, which are implemented in host memory. The nonvolatile storage device fetches the commands from the submission queues, executes the commands, and places entries in completion queues, which are also implemented in host memory, to notify the host of completion of the commands. There are typically multiple submission queues allocated by the host. Accordingly, the device controller must select from which submission queue to select the next command to be processed.
The NVMe standard, the current version of which is NVM Express, Revision 1.2, Nov. 3, 2014, the disclosure of which is incorporated herein by reference in its entirety, describes two mechanisms by which a device controller may select commands from submission queues. One mechanism is a round robin mechanism, in which the device controller selects commands from the submission queues in round robin order. Another mechanism is a weighted round robin mechanism where the submission queues are assigned static priorities or weights, and commands are selected from submission queues in round robin order using weights to determine the selection order in each round.
In either case, the next command to be fetched from a submission queue is based on static arbitration logic that either implements no priorities, as in the round robin case, or that implements only static, host-defined priorities, as in the weighted round robin case. Such static arbitration logic may be sufficient if the storage device has sufficient resources to handle all host I/O requests. However, because storage device resources may be limited and host demands on those resources may exceed the device's ability to promptly process host commands, it may be desirable to select commands to improve utilization of storage device resources.
Accordingly, there exists a need for methods, systems, and computer readable media for intelligent fetching of storage device commands from submission queues.